Calculate Dew Point Temperature

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Dew Point Temperature Calculator

Accurate Atmospheric Condensation Analysis

Celsius (°C) Fahrenheit (°F)

Calculated Dew Point

Understanding Dew Point Temperature

The dew point is the specific temperature at which air becomes saturated with water vapor. When the air temperature drops below the dew point, water vapor condenses into liquid water (dew), fog, or frost. Unlike relative humidity, which changes based on the air temperature, the dew point provides a more absolute measure of how much moisture is actually in the air.

The Magnus Formula

This calculator uses the Magnus-Tetens Approximation, which is widely recognized for its accuracy in meteorological calculations within the range of -45°C to 60°C. The formula used is:

γ(T, RH) = ln(RH/100) + [bT / (c + T)]
Tdp = [c * γ(T, RH)] / [b – γ(T, RH)]

Where constants b = 17.67 and c = 243.5 °C.

Dew Point and Human Comfort

While relative humidity is often used to describe "mugginess," dew point is actually a better indicator of how comfortable the air feels:

  • Below 50°F (10°C): Very dry and comfortable.
  • 50°F to 60°F (10-15°C): Comfortable for most people.
  • 60°F to 65°F (15-18°C): Becomes "sticky" or humid.
  • 65°F to 70°F (18-21°C): Uncomfortably humid and oppressive.
  • Over 75°F (24°C): Extremely miserable and potentially dangerous.

Example Calculation

Suppose the current temperature is 77°F (25°C) and the relative humidity is 50%.

  1. Convert Temperature to Celsius if necessary (25°C).
  2. Calculate the saturation factor (γ).
  3. Apply the Magnus coefficients.
  4. The resulting dew point would be approximately 56.9°F (13.8°C). This indicates a very comfortable environment.
function calculateDewPoint() { var airTemp = parseFloat(document.getElementById('airTemp').value); var unit = document.getElementById('tempUnit').value; var rh = parseFloat(document.getElementById('relHumidity').value); var resultDiv = document.getElementById('dewPointResult'); var resultOutput = document.getElementById('resultOutput'); var comfortText = document.getElementById('comfortLevel'); if (isNaN(airTemp) || isNaN(rh)) { alert("Please enter valid numbers for both Temperature and Humidity."); return; } if (rh 100) { alert("Relative Humidity must be between 0 and 100."); return; } // Convert to Celsius for formula var tempC = (unit === 'F') ? (airTemp – 32) * 5 / 9 : airTemp; // Magnus Formula Constants var b = 17.67; var c = 243.5; // Calculation logic var gamma = Math.log(rh / 100) + (b * tempC) / (c + tempC); var dpC = (c * gamma) / (b – gamma); var dpF = (dpC * 9 / 5) + 32; // Formatting result var displayVal; if (unit === 'F') { displayVal = dpF.toFixed(1) + " °F"; } else { displayVal = dpC.toFixed(1) + " °C"; } // Determine Comfort Level (based on Fahrenheit dew point) var comfort = ""; if (dpF = 50 && dpF = 60 && dpF = 65 && dpF = 70 && dpF < 75) { comfort = "Very Humid (Miserable)"; } else { comfort = "Extremely Oppressive (Dangerous)"; } resultOutput.innerHTML = displayVal; comfortText.innerHTML = "Air Quality: " + comfort; resultDiv.style.display = 'block'; }

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